Multi-frequency acoustic array

ABSTRACT

An apparatus comprises a substrate and transducers disposed over the substrate, each of the transducers comprising a different resonance frequency. A transducer device comprises circuitry configured to transmit signals, or to receive signals, or both. The transducer device also comprises a transducer block comprising a plurality of piezoelectric ultrasonic transducers (PMUT), wherein each of the PMUTs; and an interconnect configured to provide signals from the transducer block to the circuitry and to provide signals from the circuitry to the transducer block.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to commonly owned U.S. Pat. No.7,538,477 to R. Shane Fazzio, et al, entitled TRANSDUCERS WITH ANNULARCONTACTS and filed on Nov. 27, 2006; U.S. Pat. No. 7,538,477 to R. ShaneFazzio, et al. entitled MULTI-LAYER TRANSDUCERS WITH ANNULAR CONTACTSand filed on Apr. 19, 2007. The present application is acontinuation-in-part of U.S. patent application Ser. No. 12/261,902(U.S. Patent Application Publication 20100112965) to Osvaldo Buccafusca,et al., entitled METHOD AND APPARATUS TO TRANSMIT, RECEIVE AND PROCESSSIGNALS WITH NARROW BANDWIDTH DEVICES and filed on Oct. 30, 2008. Theentire disclosures of the cross-referenced patents and patentapplication are specifically incorporated herein by reference.

BACKGROUND

Transducers are used in a wide variety of electronic applications. Onetype of transducer is known as a piezoelectric transducer. Apiezoelectric transducer comprises a piezoelectric material disposedbetween electrodes. The application of a time-varying electrical signalwill cause a mechanical vibration across the transducer; and theapplication of a time-varying mechanical signal will cause atime-varying electrical signal to be generated by the piezoelectricmaterial of the transducer. One type of piezoelectric transducer may bebased on bulk acoustic wave (BAW) resonators and film bulk acousticresonators (FBARs). As is known, at least a part of the resonator deviceis suspended over a cavity in a substrate. This suspended area isusually referred as a membrane. As the membrane moves it translates amechanical or acoustic perturbation to an electrical signal. In asimilar manner, an electrical excitation is translated into anacoustical signal or a mechanical displacement.

Among other applications, piezoelectric transducers may be used totransmit or receive mechanical and electrical signals. These signals maybe the transduction of acoustic signals, for example, and thetransducers may be functioning as microphones (mics) and speakers andthe detection or emission of ultrasonic waves. As the need to reduce thesize of many components continues, the demand for reduced-sizetransducers continues to increase as well. This has lead tocomparatively small transducers, which may be micromachined according totechnologies such as micro-electromechanical systems (MEMS) technology,such as described in the related applications.

In many applications, there is a need to provide a transmit function ora receive function that comprises a comparatively high bandwidthtransmitter, or receiver, or both. One application where higherbandwidth devices may be useful is in the transmission and reception offast transition time signals. For example, an ideal square wave has aninfinite slope at the leading a trailing edges of each signal. As shouldbe appreciated by one skilled in the art, in the frequency domain such asignal comprises an infinite number of frequency components that aremultiple of the fundamental frequency (harmonics). Realizable squarewaves have a large number of high frequency components withdistributions around the harmonics. More complex signals have afrequency content that is not necessarily associated with harmonics. Thefrequency content of these higher complexity signals can be described byvarious types of mathematical decompositions such as Fourier, Laplace,Wavelet and others known to one of ordinary skill in the art. Totransmit or receive these fast varying signals, the transmitter orreceiver has to respond to the high frequency content. Thus, knowntransmitters and receivers require a high bandwidth to handle suchsignals.

While comparatively high bandwidth devices allow transmission andreception of signals have a broad range of frequencies, there aredrawbacks to known broadband devices. For example, known high bandwidthdevices are often more complex and more expensive to manufacture; theyare more susceptible to noise limitations and often have a comparativelylow quality (Q) factor, or simply Q. Thus, the gain of high bandwidthcomes at the expense of price and performance.

What is needed, therefore, is an apparatus that overcomes at least thedrawbacks of known transducers discussed above.

SUMMARY

In accordance with a representative embodiment, an apparatus comprises asubstrate; and transducers disposed over the substrate, each of thetransducers comprising a different resonance frequency.

In accordance with another representative embodiment, a piezoelectricultrasonic transducer (PMUT) device comprises: a substrate; transducersdisposed over the substrate, each of the transducers comprising adifferent acoustic resonance frequency. Each of the transducerscomprises a first electrode, a second electrode and a piezoelectriclayer between the first and second electrodes.

In accordance with another representative embodiment, A transducerdevice comprises circuitry configured to transmit signals, or to receivesignals, or both. The transducer device also comprises a transducerblock comprising a plurality of piezoelectric ultrasonic transducers(PMUT), wherein each of the PMUTs; and an interconnect configured toprovide signals from the transducer block to the circuitry and toprovide signals from the circuitry to the transducer block.

BRIEF DESCRIPTION OF THE DRAWINGS

The present teachings are best understood from the following detaileddescription when read with the accompanying drawing figures. Thefeatures are not necessarily drawn to scale. Wherever practical, likereference numerals refer to like features.

FIG. 1 shows a simplified block diagram of a transducer device inaccordance with a representative embodiment.

FIG. 2A shows a cross-sectional view of a MEMs transducer in accordancewith a representative embodiment.

FIG. 2B shows a top view of the MEMs device in accordance with arepresentative embodiment.

FIG. 3 shows the MEMs device in accordance with another representativeembodiment.

FIG. 4 shows a MEMs device in cross-section in accordance with arepresentative embodiment.

FIG. 5A shows a MEMs device in cross-section in accordance with arepresentative embodiment.

FIG. 5B shows a top-view of a MEMs in accordance with a representativeembodiment.

FIG. 6A shows a MEMs device in cross-section in accordance with arepresentative embodiment.

FIG. 6B shows a top view of a MEMs device in accordance with arepresentative embodiment.

FIG. 7 shows a MEMs device in cross-section in accordance with arepresentative embodiment.

FIG. 8A shows a MEMs device in cross-section in accordance with arepresentative embodiment.

FIG. 8B shows a top view of the MEMs device depicted in FIG. 8A.

FIG. 9A shows a MEMs device in cross-section in accordance with arepresentative embodiment.

FIG. 9B shows a top view of a MEMs device in accordance with arepresentative embodiment.

FIG. 10 shows a MEMs device in cross-section in accordance with arepresentative embodiment.

FIG. 11 shows a top view of a MEMs device in accordance with arepresentative embodiment.

FIG. 12 shows a cross-sectional view of the MEMs device depicted in FIG.11.

DEFINED TERMINOLOGY

As used herein, the terms ‘a’ or ‘an’, as used herein are defined as oneor more than one.

In addition to their ordinary meanings, the terms ‘substantial’ or‘substantially’ mean to with acceptable limits or degree to one havingordinary skill in the art. For example, ‘substantially cancelled’ meansthat one skilled in the art would consider the cancellation to beacceptable.

In addition to their ordinary meanings, the terms ‘approximately’ meanto within an acceptable limit or amount to one having ordinary skill inthe art. For example, ‘approximately the same’ means that one ofordinary skill in the art would consider the items being compared to bethe same.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation andnot limitation, representative embodiments disclosing specific detailsare set forth in order to provide a thorough understanding of thepresent teachings. Descriptions of known devices, materials andmanufacturing methods may be omitted so as to avoid obscuring thedescription of the representative embodiments. Nonetheless, suchdevices, materials and methods that are within the purview of one ofordinary skill in the art may be used in accordance with therepresentative embodiments.

FIG. 1 shows a simplified block diagram of a transducer device 100 inaccordance with a representative embodiment. The transducer device 100comprises transmit/receive circuitry 101, an interconnect 102 and atransducer block 103.

The transmit/receive circuitry 101 comprises components and circuits asdescribed in the parent application to Buccafusca, et al. Notably, thetransducer device 100 may be configured to operate in a transmit mode orin a receive mode, or in a duplex mode. As such, the transmit/receivecircuitry 101 may be configured to provide an input signals to thetransducer block 103 in a manner described in the parent application inthe transmit mode; or may be configured to receive output signals fromthe transducer block 103 as described in the parent application is areceive mode; or may be configured to provide input signals to thetransducer block 103 and receive signals from the transducer block 103in a duplex mode. Generally, the transmit/receive circuitry 101illustratively comprises a singled-ended, differential or common-modeimplementation of digital and analog signal manipulation andconditioning, filtering, impedance matching, phase control, switching,and the like. This implementation can be realized with discretecomponents or integrated in a semiconductor chip.

The interconnect 102 comprises the electrical interconnection betweenthe driver circuitry and the transducer block 103. The interconnect 102may contain one or more signal paths and encompasses the varioustechnologies such as wire bonding, bumping or any other joining orwiring technique.

As described more fully herein, the transducer block 103 comprises asingle transducer configured to operate at more than one resonantfrequency, or comprises a plurality of transducers, each operating at aparticular resonant frequency.

The transmit/receive circuitry 101, the interconnect 102 and thetransducer block 103 may be instantiated on a common substrate, or maybe instantiated one or more individual components or a combinationthereof. As will become clearer as the present description continues,the present teachings contemplate fabrication of the transducer device100 in large-scale semiconductor processing on a common semiconductorsubstrate, or via individual chips on a common substrate, for example.Further packaging of the transducer device 100 is also contemplatedusing known methods and materials.

The embodiments described below relate to MEMs devices comprisingtransducers contemplated for use in the transducer block 103. In keepingwith the teachings above, the MEMs devices may be provided on adedicated substrate (e.g., as a stand-alone chip or package), or may beintegrated into a substrate common to the interconnect 102, or thetransmit/receive circuitry 101, or both.

FIG. 2A shows a cross-sectional view of a MEMs device 200 in accordancewith a representative embodiment. The MEMs device 200 comprises atransducer 201 disposed over a substrate 202. The transducer 201comprises a first electrode 203, a piezoelectric element 204 and asecond electrode 205. The transducer 201 may be one of the transducersprovided in the transducer block 103, and the substrate 202 may becommon to the plurality of transducers in the transducer block 103.Notably, a portion of each transducer 201 is provided over a cavity (notshown in FIG. 2A) in the substrate 202. Often, this portion of thetransducer is referred to as a membrane. The membrane is configured tooscillate by flexing (i.e., in a flexure mode) over a substantialportion of the active area thereof.

Illustratively, the transducer 201 comprises one embodiment of apiezoelectric micromachined ultrasonic transducer (pMUT) described inaccordance with the present teachings. PMUTs are illustratively based onfilm bulk acoustic (FBA) transducer technology or bulk acoustic wave(BAW) technology. As described more fully herein, a plurality of PMUTsin accordance with the representative embodiments may be provided over asingle substrate. Moreover, in representative embodiments, the PMUTs aredriven at a resonance condition, and thus may be film bulk acousticresonators (FBARs). Regardless of the structure(s) of the transducer 201selected, the transducer(s) 201 are contemplated for use in a variety ofapplications. These applications include, but are not limited tomicrophone applications, ultrasonic transmitter applications andultrasonic receiver applications.

The piezoelectric element 204 of the representative embodiments maycomprise one or more layers of piezoelectric material including AN, PZTZnO or other suitable piezoelectric material that can be instantiated ina substantially thin film layer. The first and second electrodes 203,205 comprise materials such as molybdenum, aluminum, copper, gold,platinum, tungsten, silver, titanium and other electrically conductiveor partially conductive materials, their alloys and their combination.The first and second electrodes 203, 205 extend to contacts that allowinterconnection to the driver circuitry. Moreover, the substrate 202comprises a material selected for electrical, or thermal, or integrationproperties, or a combination thereof. Illustrative materials includesilicon, compound semiconductors materials (such as Gallium-Arsenide,Indium-Phosphide, Silicon-Carbide, Cadmium Zinc Telluride, et cetera),glass, ceramic alumina suitably selected material that can be providedin wafer form.

Additional details of the transducer 201 implemented as a pMUT aredescribed in the referenced applications to Fazzio, et al. Moreover, thetransducer 201 may be fabricated according to known semiconductorprocessing methods and using known materials. Illustratively, thestructure of the MEMs device 200 may be as described in one or more ofthe following U.S. Pat. No. 6,462,631 to Bradley, et al.; U.S. Pat. Nos.6,377,137 and 6,469,597 to Ruby; U.S. Pat. No. 6,472,954 to Ruby, etal.; and may be fabricated according to the teachings of U.S. Pat. Nos.5,587,620, 5,873,153 and 6,507,983 to Ruby, et al. The disclosures ofthese patents are specifically incorporated herein by reference. It isemphasized that the structures, methods and materials described in thesepatents are representative and other methods of fabrication andmaterials within the purview of one of ordinary skill in the art arecontemplated.

FIG. 2B shows a top view of the MEMs device 200 in accordance with arepresentative embodiment. In the present embodiment, the firstelectrode 203 is substantially circular in shape. The circular shape isillustrative and it is emphasized that the first and second electrodes203, 205 may be elliptical, rectangular and any other regular orirregular polygonal shape. Contacts 206, 207 are configured to contact arespective one of the first and second electrodes 203, 205.Illustratively, the contacts provide the interconnection to thetransmit/receive circuitry 101, and depending on the mode of operation,are configured to provide the drive signal(s) to the MEMs device 200 orto provide the receive signal from the MEMs device 200, or both.

FIG. 3 shows the MEMs device 200 in accordance with anotherrepresentative embodiment. In the present embodiment, the firstelectrode 203 and the second electrode (not shown in FIG. 3) areapodized. The apodization of first and second electrodes 203, 205improves the quality factor (Q) of the MEMs device 200 by reducinglosses to transverse modes. Apodization is described for example incommonly owned U.S. patent application Ser. No. 11/443,954 entitled“PIEZOELECTRIC RESONATOR STRUCTURES AND ELECTRICAL FILTERS” to RichardC. Ruby. The disclosure of this application is specifically incorporatedherein by reference.

As described above, contacts 206, 207 are configured to contact arespective one of the first and second electrodes 203, 205.Illustratively, the contacts provide the interconnection to thetransmit/receive circuitry 101, and depending on the mode of operation,are configured to provide the drive signal(s) to the MEMs device 200 orto provide the receive signal from the MEMs device 200, or both.

FIG. 4 shows a MEMs device 400 in cross-section in accordance with arepresentative embodiment. The MEMs device comprises a transducer 401disposed over a substrate 402. The transducer 401 comprises electrodes403 and piezoelectric elements 404 between respective electrodes to fora two layer stack. Notably, additional electrodes and piezoelectricelements can be provided for additional stacks. The stacks can beelectrically connected in series or in parallel, such as described inthe referenced application to Fazzio, et al., entitled MULTI-LAYERTRANSDUCERS WITH ANNULAR CONTACTS. The selective series connection ofthe stacks usefully cause the phase of the flexure mode of theindividual stacks to be substantially the same in order to increase theamplitude of the flexing of the transducer 401 and thus the transduceroutput. Parallel connections can be made to provide noise cancellation,for example.

FIG. 5A shows a MEMs device 500 in cross-section in accordance with arepresentative embodiment. The MEMs device comprises a transducer 501disposed over a substrate 502. The transducer 501 comprises first andsecond electrodes 203, 205 and a piezoelectric element 204 between thefirst and second electrodes 203, 205. Notably, and as shown more clearin the top view in FIG. 5B, the first electrode 203 is disposedannularly over the piezoelectric element 204. This ring-like shape incontrast the second electrode 205, which is substantially circular inshape. As noted before the circular shape of either the ring-like shapeof the first electrode 203 or the circular shape of the second electrode205 is merely illustrative, and other shapes, such as elliptical shapes,with the first electrode 203 being annular and elliptical and the secondelectrode 205 being areally an ellipse are contemplated. Further detailsincluding various embodiments of annularly disposed electrodes and theirelectrical connections are described in the referenced application toFazzio, et al., entitled MULTI-LAYER TRANSDUCERS WITH ANNULAR CONTACTS.

FIG. 6A shows a MEMs device 600 in cross-section in accordance with arepresentative embodiment. The MEMs device 600 comprises a transducer601 disposed over a substrate 602. The transducer 601 comprises firstand second electrodes 203, 205 and a piezoelectric element 204 betweenthe first and second electrodes 203, 205. Notably, and as shown moreclear in the top view in FIG. 6B, the first electrode 203 issubstantially circular have an areal dimension that is less than theareal dimension of the piezoelectric element 204 and the secondelectrode 205. Illustratively, the piezoelectric element 204 and thesecond electrode 205 are also substantially circular, and havesubstantially identical areal dimensions. As described above, thecircular shapes of the electrodes and the piezoelectric element may beother than circular.

FIG. 7 shows a MEMs device 700 in cross-section in accordance with arepresentative embodiment. The MEMs device 700 comprises a transducer701 disposed over a substrate 202. The transducer 701 comprises firstand second electrodes 203, 205 and a piezoelectric element 204 betweenthe first and second electrodes 203, 205. The shape of the first andsecond electrodes 203, 205 and the piezoelectric element 204 may be asdescribed above in connection with representative embodiment. The MEMsdevice 700 comprises a cavity 703 with an opening at a first surface 702of the substrate 202, but not extending through a second surface 704 ofthe substrate. The cavity 703 provides damping of the transducer 701,and thus provides a damped resonator structure. As discussed above, theportion of the transducer 701 that is suspended over the cavity 703comprises the membrane.

The cavity 703 may be formed in much the same manner as a known‘swimming pool’ in an FBAR, and as disclosed in certain referencedpatents above. However, the dimensions of the cavity are controlled tomanipulate the acoustic response of the transducer 701. Generally, thedimensions of the cavity 703 are selected to manipulate the acousticproperties of the transducer. Usefully the cavity 703 has a depth ofλ/4, where λ is the wavelength of the acoustic wave in air. Selection ofa cavity depth of λ/4 fosters vibration of the membrane vibration andproduce a comparatively higher Q-factor and increased efficiency in thetransducer 701.

FIG. 8A shows a MEMs device 800 in cross-section in accordance with arepresentative embodiment. FIG. 8B shows a top view of the MEMs devicedepicted in FIG. 8A. The MEMs device 800 comprises a transducer 801disposed over a substrate 202. The transducer 801 comprises first andsecond electrodes 203, 205 and a piezoelectric element 204 between thefirst and second electrodes 203, 205. The shape of the first and secondelectrodes 203, 205 and the piezoelectric element 204 may be asdescribed above in connection with representative embodiments. The MEMsdevice 800 comprises cavity 703 with vent 803 at a first surface 802 ofthe substrate 202, but not extending through a second surface 804 of thesubstrate. As discussed above, the portion of the transducer 801 that issuspended over the cavity 703 comprises the membrane.

The vent 803 is formed between the cavity 703 and the first surface 802to promote pressure equalization between the cavity 703 and the ambientof the MEMs device 800. As noted previously, the cavity 703 may beformed in much the same manner as a known ‘swimming pool’ in an FBAR,and as disclosed in certain referenced patents above. Again, thedimensions of the cavity are controlled to manipulate the acousticresponse of the transducer 801. The vent 803 is created by one of avariety of wet or dry etching methods known in the art, and is selectedbased on substrate material, aspect ratio and overall compatibility withoverall processing steps used in fabricating the MEMs device 800.

FIG. 9A shows a MEMs device 900 in cross-section in accordance with arepresentative embodiment. The MEMs device 900 comprises a transducer901 disposed over the substrate 202. The transducer 901 comprises firstand second electrodes 203, 205 and the piezoelectric element 204 betweenthe first and second electrodes 203, 205. The first and secondelectrodes 203, 205 and the piezoelectric element 204 are successivelystacked and annular in shape about a vent 903 that extends through thefirst and second electrodes 203, 205 and the first surface 902 of thesubstrate 202, and into the cavity 703. The cavity 703 does not extendthrough a second surface 904 of the substrate 202. Notably, the annularor ring-shape of the first and second electrodes 203, 205 and thepiezoelectric element 204 are shown more clearly in FIG. 9B. The vent903 promotes pressure equalization between the cavity 703 and theambient of the MEMs device 900. The vent 903 fosters pressureequalization between the sides (front and back) of the membrane. Asnoted previously, the cavity 703 may be formed in much the same manneras a known ‘swimming pool’ in an FBAR, and as disclosed in certainreferenced patents above. Again, the dimensions of the cavity arecontrolled to manipulate the acoustic response of the transducer 801.The vent 903 is created by one of a variety of wet or dry etchingmethods known in the art, and is selected based on substrate material,aspect ratio and overall compatibility with overall processing stepsused in fabricating the MEMs device 800.

FIG. 10 shows a MEMs device 1000 in cross-section in accordance with arepresentative embodiment. The MEMs device 1000 comprises a transducer1001 disposed over the substrate 202. The transducer 1001 comprisesfirst and second electrodes 203, 205 and the piezoelectric element 204between the first and second electrodes 203, 205. The first and secondelectrodes 203, 205 and the piezoelectric element 204 may be one of avariety of shapes, such as described in connection with respectiveembodiments above. However, there is no vent included in the MEMs device1000 at least because an opening 1003 is provided from a first surface1002 through the substrate 202 and through a second surface 1004. Likethe cavity 703 described previously, the opening 1003 is disposedbeneath the second electrode 205. The opening 1003 may be formed in muchthe same manner as a known ‘swimming pool’ in an FBAR, and as disclosedin certain referenced patents above. The dimensions of the opening 1003are controlled to manipulate the acoustic response of the transducer1001. For emission on both sides of the membrane of the transducer 1001,the opening 1003 is selected to be comparatively large; illustrativelyon approximately a diameter of the membrane. For top side emission, thediameter is selected to provide the necessary acoustic damping tomanipulate Q (the smaller the diameter, the higher the acousticresistance and the smaller the Q). The placement of the opening 1003 is,in both cases, centered with the membrane

The opening 1003 provides pressure equalization of both sides of thetransducer 1001 thereby eliminating the need for use of a vent.Moreover, the transducer 1001 may transmit and receive acoustic wavesthrough opening 1003, as well as from the opposing side of thetransducer 1001 (i.e., at the interface of the first electrode 203 andthe ambient). Thus, the transducer 1001 can function in both the +y andthe −y directions according to the coordinate system shown in FIG. 10.

The MEMs devices described in connection with the representativeembodiments commonly comprise a transducer that comprises a membranethat deflects or vibrates due to acoustic pressure; thus the response isa flexure mode. Varying the geometry (size, shape and thickness) of thetransducers allow the tuning to different frequencies.

FIG. 11 shows a top view of a MEMs device 1100 in accordance with arepresentative embodiment. The MEMs device 1100 comprises a plurality oftransducers 1102, 1103, 1104 forming an array of transducers. The arrayof transducers may be provided on a common substrate, forming atransducer block. The transducer block may then be connected tocircuitry (e.g., a driver circuit) suitable for signal transmission orreception, or both. Alternatively, the MEMs device 1100 may comprise aplurality of individual transducer not provided on a common substrate,and connected to circuitry. Regardless of whether the transducers areprovided on a common substrate as a transducer block, or individualtransducers, the transducers of the array of the MEMs device 1100 may beone or more of the transducers described above in connection withrepresentative embodiment. Notably, while in some embodiments thetransducers 1102, 1103, 1104 are of the same or similar structure, thisis not required. For example, one transducer may be an apodizedstructure such as described in connection with the embodiments of FIG.3, while others may have circular or annular electrodes as described inconnection with embodiments of FIG. 1, 4, 5A or 6A, for example.Moreover, vents and openings as described above may be implemented inone or more of the transducers 1102, 1103, 1104. Finally, theimplementation of three transducers in the array is merely illustrative,and more or fewer transducers may be provided in the MEMs device 1100.Incidentally, FIG. 12 shows a cross-section of the MEMs device 1100 ofFIG. 11 of a representative embodiment including transducers 1104 and1102 respectively over cavities 703 and 704, and each respectivelyhaving a stack including a first electrode, a piezoelectric element anda second electrode.

While the transducers 1102, 1103, 1104 share certain commoncharacteristics, their resonance condition and thereby their resonancefrequencies are generally not the same. Rather, each transducer 1102,1103, 1104 of the array can be engineered to operate in differentacoustic frequencies selected to modify the frequency response.

As would be appreciated by one of ordinary skill in the art, theparameters of the transducers 1102, 1103,1104 that impact thecharacteristic frequency depend on (among other factors) the thicknessof the layers of the transducer stack and the diameter of the membrane.In a representative embodiment, different transducer frequencies can beeffected by selecting the thickness of the electrodes and piezoelectriclayers of each transducer to be substantially the same, but the diameterof the membranes to be different. The devices in the array could bedriven independently or simultaneously as described in the filedapplication to Buccafusca, et al., and may be interconnected in seriesand/or in parallel.

In one representative embodiment, the transducers 1102, 1103 and 1104for a harmonic array. The transducers 1102, 1103, 1104 are selected tohave different sizes, or shapes, or both as noted above to improve theharmonic emission. Notably, because each transducer 1102, 1103 and 1104transmit at its particular resonance frequency, in order to transmitadditional frequency content it is necessary to add more transducers atthe desired frequency.

In operation, a transducer block comprising a plurality of transducers1102, 1103, 1104 are provided on a common substrate, or a plurality ofindividual transducer are provided to for the array. In a representativeembodiment, the transducers 1102, 1103, 1104 are the connected totransmit circuitry or receive circuitry, or both, such as described inthe parent application entitled “METHOD AND APPARATUS TO TRANSMIT,RECEIVE AND PROCESS SIGNALS WITH NARROW BANDWIDTH DEVICES.” Thetransducers 1102, 1103, 1104 may be interconnected in series and/or inparallel. In keeping with the description of the representativeembodiments, the sizes of the emitters can be selected to match thefundamental and the odd harmonic frequencies to reproduce better squarewaves in the time domain. It is emphasized that the transmit/receivecircuitry described in this application is merely illustrative, and useof other transmit and receive circuitry is contemplated.

In view of this disclosure it is noted that the MEMs devices,transducers and apparatuses can be implemented in a variety ofmaterials, variant structures, configurations and topologies. Moreover,applications other than small feature size transducers may benefit fromthe present teachings. Further, the various materials, structures andparameters are included by way of example only and not in any limitingsense. In view of this disclosure, those skilled in the art canimplement the present teachings in determining their own applicationsand needed materials and equipment to implement these applications,while remaining within the scope of the appended claims.

The invention claimed is:
 1. An apparatus, comprising: a substrate; andtransducers disposed over the substrate, each of the transducers beingconfigured to operate at a different resonance frequency, wherein atleast one of the transducers is disposed over a cavity and comprises avent between the cavity and an opposing surface of the transducer, andthe vent is configured to substantially equalize a pressure between thecavity and an ambient environment to the opposing surface, wherein thetransducer frequencies are selected in combination to transmit asubstantially square wave output signal, or to receive a substantiallysquare wave input signal.
 2. An apparatus as claimed in claim 1, whereineach of the transducers comprises a first electrode, a second electrodeand a piezoelectric layer between the first and second electrodes.
 3. Anapparatus as claimed in claim 1, wherein the vent extends through thetransducer to the cavity.
 4. A piezoelectric ultrasonic transducer(PMUT) device, comprising: a substrate; and transducers disposed overthe substrate, each of the transducers being configured to operate at adifferent acoustic resonance frequency, wherein each of the transducerscomprises a first electrode, a second electrode and a piezoelectriclayer between the first and second electrodes, wherein the resonancefrequencies are selected in combination to transmit a substantiallysquare wave output signal, or to receive a substantially square waveinput signal.
 5. A PMUT as claimed in claim 4, wherein a portion of eachtransducer is provided over a cavity in the substrate, wherein theportion of the transducer comprises a membrane.
 6. A PMUT as claimed inclaim 5, wherein at least one of the transducers further comprises avent between the cavity and an opposing surface of the transducer, andconfigured to substantially equalize a pressure between the cavity andan ambient to the opposing surface.
 7. A PMUT as claimed in claim 6,wherein at least one of the transducers further comprises a vent thatextends through the transducer to the cavity.
 8. A transducer device,comprising: circuitry configured to transmit signals, or to receivesignals, or both; a transducer block comprising a plurality ofpiezoelectric ultrasonic transducers (PMUT) disposed over the substrate,each of the transducers being configured to operate at a differentresonance frequency, wherein at least one of the PMUTs is disposed overa cavity and comprises a vent between the cavity and an opposing surfaceof the PMUT, and the vent is configured to substantially equalize apressure between the cavity and an ambient environment to the opposingsurface; and an interconnect configured to provide signals from thetransducer block to the circuitry and to provide signals from thecircuitry to the transducer block, wherein the resonance frequencies areselected in combination to transmit a substantially square wave outputsignal, or to receive a substantially square wave input signal.
 9. Atransducer device as claimed in claim 8, wherein each of the PMUTs isconfigured to operate at a different acoustic resonance frequency.
 10. Atransducer device as claimed in claim 9, wherein each of the PMUTs areprovided over a common substrate.
 11. A transducer device as claimed inclaim 9, wherein each of the PMUTs is separate from the other PMUTs.